Facies and depositional environments of the Devonian-Carboniferous succession of Iraq

Facies associations and depositional environments of the Late Devonian-Early Carboniferous succession in Iraq have been studied in several boreholes from north and northwestern Iraq. The >400 m-thick succession comprises the Kaista, Ora, Harur and Raha formations which are composed generally of mixed siliciclastic-carbonate facies. The Kaista Formation consists of sandstones intercalated with siltstones and calcareous shale that were deposited in a mixed fluvial-marine environment. The Ora Formation is composed dominantly of black shale with subordinate sandstone and dolomite deposited in a shallow-marine, sub-tidal shelf environment. The Harur Formation is composed mainly of dolomite with subordinate shale and was deposited in a deep sub-tidal environment. The Raha Formation consists mainly of marine shales intercalated with sandstones and concluded the Kaskaskia megasequence. The depositional setting is considered as a subsiding basin with a wide geographic distribution. It extended from the Ora region in the extreme north of Iraq to west and southwestern Iraq and reflects an epicontinental or epeiric sea setting on a homoclinal ramp inclined to the southeast. Copyright (C) 2008 John Wiley & Sons, Ltd.